The claimEvidence A · guideline-tier
Willpower is a fuel tank that drains as you use it
The evidence
The ego-depletion model — the idea that willpower drains like a tank — failed a preregistered replication across 23 labs (effect size d=0.04, Hagger 2016); design your environment, don't white-knuckle it.
The mechanism, in brief
A popular idea holds that willpower is like a fuel tank: every use drains it, so if you use it up in the morning you cannot resist snacks in the evening. In the most rigorous test it has faced, this ego depletion model produced almost no measurable effect.
Sources (1)
- Hagger, M. S., Chatzisarantis, N. L. D., et al. (2016). A multilab preregistered replication of the ego-depletion effect. Perspectives on Psychological Science, 11(4), 546-573. Across 23 labs (N = 2,141) the pooled ego-depletion effect was d = 0.04 (95% CI -0.07 to 0.14), not different from zero.